Each one has its individual 4473 for the date the transaction was initiated. One NICS check won't work for all the rest of them. They're holding the rest because they don't want to be boned on federal paperwork...
I'm no lawyer, but if I'm reading the ATF guidelines correctly, for regulated purchases in MD, an FFL does not need an NTN to release after 7 days have passed. If no response is received by 3 days in their (ATF) book then its an assumed proceed.
Lets take the example nationwide. Lets say some hacker group slipped a trojan or virus into the NICS system deleting all their information. They don't know who should and shouldn't have a firearm now so they can't give an answer in 3 days, but their rule book says automatic release after 3 days, so no NTN. Do you think the entire country is going to be ok with their firearm purchases being queued indefinitely until NICS is back online because that is exactly what is going on in MD.
The ATF saying don't release without an NTN because of unusual circumstances is like a tenant telling his landlord he will be late with the rent because his boss did not pay him on time. That issue is between you and your boss and your landlord could care less. They designed the system and it should not be us (or the FFL) that is punished because they can't get the left hand to talk to the right hand using instant message instead of smoke signals.